Objectives
Using the European Health Interview Survey (EHIS) questionnaire, a web-based survey was organized alongside a face-to-face (F2F) survey including a paper-and-pencil (P&P) questionnaire for sensitive topics. Associated with these different modes, other design features varied too (e.g., recruitment, incentives, sampling). We assessed whether these whole data collection systems developed around the modes produced equivalent health estimates.

Methods
Data were obtained from two population-based surveys: the EHISWEB (web-administered, n = 1010) and the Belgian Health Interview Survey 2018 (BHIS2018) (interviewer-administered, n = 2748). Logistic regression analyses were used to assess mode system differences while adjusting for socio-demographic differences in the net samples.

Results
For the P&P mode of the BHIS, significant mode system differences were detected for 2 of the 9 health indicators. Among the indicators collected via the F2F mode, 9 of the 18 indicators showed significant differences.

Conclusions
Indicators collected via the web-based and P&P self-administered modes were generally more comparable than indicators collected via the web-based and F2F mode. Furthermore, fewer differences were detected for indicators based on simple and factual questions compared to indicators based on subjective or complex questions.